The use of straddle-type blueberry picking machines is well known today. These machines employ a substantially U-shaped elevated ground contacting frame which is usually self-propelled. The fruit bearing bushes are usually planted in spaced rows. The machine then straddles each row with the blueberry bushes passing through a longitudinal opening in the center of the machine. In order to dislodge the ripened berries from the branches of the bush, arms have been used which project out from each side into the longitudinal opening to agitate the bushes as the machine moves along the row. Others have suggested the use of freely rotating spaced drums with fingers projecting from the outer surface which roll along the bush at the same speed as the harvesting machine passes over the ground. The drums are biased inwardly to force the drums into contact with the surface of the bushes. Fingers projecting from the drums comb the surface of the bushes and knock the ripened berries off the branches.
In this description, blueberries and blueberry bushes will be used as a representative crop bearing bush. The invention, however, is not so limited. The term "blueberry" is used as a generic expression for all types of berries, fruits, beans, nuts, vegetables, and the like, which grow on bushes, trees and vines and which can be harvested mechanically by a machine passing over the crop bearing plant.
In order to improve the harvesting with straddle-type harvest machines employing freely rotating shakers or brush-like members, means have been used to cause the shakers to vibrate or twist as they roll along the bushes. For example, Rust U.S. Pat. No. 3,184,908 has a pair of laterally and longitudinally spaced, vertically oriented shakers fixed to a ground contacting frame. A pair of spaced crankshafts connected by an endless chain extend across the top of the frame. Each shaker is rotatably connected to 180.degree. opposed cranks on the crankshafts. The crankshafts are driven by a power take off from a tractor which causes the shakers to move up and down as the shakers roll along in contact with the fruit bearing plants. When using this type of assembly, the drive mechanism for the shakers can be loaded down when the rods or fingers on each shaker enter into a bush with heavy vegetation. Also, the shaker assembly is directly attached to the frame which can cause substantial vibration of the frame during operation of the picker.
Christie et al. U.S. Pat. Nos. 3,325,984 and 3,385,042 disclose a straddle-type picker having a pair of freely rotatable drums which support a plurality of projecting bush contacting and penetrating fingers. Each of the drums is freely rotatable and moves along the row of bushes at the same rate that the frame of the machine passes over the ground. Each of the shakers has its own vibrating unit which rotates an eccentric connected to the central shaft of the drum. Both the frequency and amplitude of the motion of the shakers is manually adjustable by changing the position of mechanical linkages. Again, as in the previously described picker, the picking action can be erratic, depending upon the density of the vegetation in the bush. Also, drum-type pickers have a tendency to roll along the surface of the bush combing the branches stripping all of the berries and scraping the branches, damaging the plants.
Weygandt et al. U.S. Pat. No. 3,494,117 discloses a straddle-type picker having a pair of spaced drums supporting a plurality of fingers for contacting and dislodging the fruit from the bushes. The drums of Weygandt et al. are supported either on heavy coil springs or by spring arms. The drums are caused to vibrate through the use of rotating weights mounted within the drums. As the weights rotate simultaneously in the same direction, the drums move in an orbital manner. The orbital movement can cause thin branches to wrap around the fingers resulting in damage to the bushes.
In each of the aforementioned references, the entire shaker assemblies can be made to move laterally relative to the plants being harvested. In Rust, the shakers are manually movable while in Christie et al., the shakers are spring biased to extend toward the longitudinal centerline of the machine. In Weygandt et al. the shakers are mounted on powered movable arms. In each of the referenced systems, the shaker or picker has a tendency to comb the outer surface of each bush.
It is extremely important in harvesting blueberries that the proper amount of energy be applied to each bush so that only the ripened fruit is collected, leaving the green or not yet fully ripened fruit for picking at another time. It is also important that the bushes be protected from damage during the harvesting process. In the past, the rows of blueberry bushes being harvested were slapped by flailing arms or radically oscillating shaker drums which produced a complex series of motions in the hope of striking all of the berry bearing branches to pick the fruit. The erratic oscillations of the pickers caused not only unripe berries to be picked but also the bushes themselves to be damaged.